1. Field of the Invention
The present invention relates to a method of forming a shallow trench isolation device, in particular, to a method of forming a shallow trench isolation device in order to prevent kick effects.
2. Description of the Prior Art
As device technology is scaled down to the quarter micron region, the use of conventional local oxidation of silicon (LOCOS) isolation is confined by smaller channel-width encroachment (bird's beak). Shallow trench isolation (STI) can be used to eliminate these encroachments, especially in ultra large scale integrated (ULSI) circuit devices.
Therefore, the shallow trench isolation (STI) method has been developed for highly integrated circuits, and sub-half micron integrated circuits in particular. A shallow trench isolation (STI) structure is formed by performing an anisotropic etching operation using a silicon nitride hard mask to form a steep-sided trench in a semiconductor substrate. Oxide material is deposited into the trench to form an oxide plug. However, the aforementioned method of STI fabrication often results in the formation of recess cavities, resulting in a locally intensified electric field. This leads to an abnormal sub-threshold current leakage in the transistor channel, resulting in the intensification of the kick effect. As shown in FIG. 1, a trench 12 is formed in a semiconductor substrate 10. A pad oxide layer 14 is formed in the surface of the trench 12 and an oxide 16 is filled therein, thereby forming a shallow trench isolation device. During this process, after forming the conventional trench devices, a recess phenomenon is usually formed on the corner structure 18 due to the dishing of the liner oxide layer 14 and the oxide 16. In the subsequent process, polysilicon and other materials are filled in the recess on the corner structure 18, thereby reducing the threshold voltage (Vt) and diverging a specific value of device. Therefore, the electrical quality of the device is reduced and a kick effect occurs in the device.
In the view of this, the present invention provides a method of forming a shallow trench isolation device in order to prevent kick effects in order to overcome the above-mentioned disadvantages.